Hello Gabriel,

Classically, LF/HF is understood as an index of sympathovagal balance, since the powers at LF and HF bands are assumed to be the result of sympathetic and parasympathetic modulation to the heart, respectively. However, there are some caveats on it that we should be aware of.

1) LF band is not exclusively the result of sympathetic modulation. It is recognized that vagal modulation can also affect the power at this band;

2) In general, the absolute power at HF band is a good index of cardiac vagal modulation. However, as it is driven by respiration, if the respiratory frequency is lower than 0.15 Hz (the limit between LF and HF band), HF power will not account for vagal modulation and the power at LF band will be highly biased.

Below are some suggestions for readings. I hope it helps.

Best,

Luiz

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Dear Luiz Eduardo Virgilio Silva,

Thank you for such explanation. I have read some of the recommendations and also included more subjects in the present analysis. I'm considering using the absolute HF power, however, how can I access the respiration frequency in order to avoid misinterpretation? I'm currently using a V800 Polar to collect these data.

Thank you again,

Gabriel.

Hi Gabriel Palmeira Paschoalino,

When the respiratory signal is not recorded, it can be derived from the ECG signal, since respiration influences the amplitude of R-peaks. There are some algorithms proposed for it. However, I suppose Polar does not give the ECG signal, only the tachogram. Using only the tachogram, I think it is not possible to derive the respiration.

Luiz Eduardo Virgilio Silva

I thought so. In this case, I am considering using different variables, such as RMSSD (ms) of RR intervals. Values are higher during baseline and low conditions compared to high anxiety conditions. Would you expect the same?

Yes, it makes sense if we consider that anxiety is characterized by increased sympathetic modulation. However, you must bear in mind that RMSSD captures the mean magnitude changes from one beat to the next and is somewhat correlated to HF power. Thus, if the respiratory frequency decreases, a lower respiratory sinus arrhythmia may also affect RMSSD.

From your experience, do you think those conditions may change the respiratory frequency?

Considering that daily (not racing or enduro) driving is way more cognitive than physically demanding, I would expect small but not great changes in the respiratory frequency. Besides the anxiety manipulation, experience is also different between groups, and it could modulate how anxiety affects ANS response. However, it is just a guess, because these are such novel variables to me.

I see. Well, considering that the limit between LF and HF band is 0.15 Hz for humans, the use of HF power as an index of vagal modulation would become a problem when respiration was lower than 9 bpm. You can assume that it will not occur in your protocol and state it as a possible limitation of the study.

In addition to classical time and frequency domain parameters, you can also calculate some nonlinear indices from HRV series, such as entropy and DFA. Although their meaning are not much clear regarding physiological mechanisms, they have been used for risk stratification. They are implemented in Kubios as well.

Best,

Luiz

Your comments were of great value, Luiz Eduardo Virgilio Silva .

Soon, I will assemble these data with other measures, such as pupillometry. Let's see what we find out. Thank you very much.

Gabriel.

How to interpret LF/HF ratio in slow breathing (0.1Hz) condition? I assume it will be vagal to sympathetic balance?

In the case of breathing at 0.1Hz, the LF/HF ratio is meaningless. To interpret the LF/HF ratio as an index of sympathovagal balance, the respiratory frequency must be higher than 0.15Hz.

But previous papers did not consider it as meaningless. "After the breathing exercise, the RF group reported higher positive mood than the other two groups and a significantly higher LF/HF HRV ratio relative to the control group, a key goal in HRVB training (p 

Luiz Eduardo Virgilio Silva

The Impact of Resonance Frequency Breathing on Measures of Heart Rate Variability, Blood Pressure, and Mood

Dear Debanjan Borthakur

When I said that LF/HF ratio is meaningless, I meant it is for the wide-sense classical interpretation of LF/HF as a sympathovagal balance marker. I don't know anything about biofeedback training and, in this context, they may use this index with a different interpretation.

If you look at Figure 1 of the paper you mentioned, you will notice that LF/HF is increased during the slow breathing period. However, it does not mean that sympathetic modulation increased compared to vagal (respiratory) modulation. Since the respiratory frequency is lower than 0.15Hz, the respiratory sinus arrhythmia (vagal modulation) falls within the LF band. Therefore, both sympathetic and vagal modulations are accounted for in the LF band and the LF/HF ratio does not represent a marker of sympathovagal balance.

If you see another interpretation of this index in the context of biofeedback training, please share it with us.

Best regards,

Luiz

Luiz Eduardo Virgilio Silva Hi Luiz in slow breathing condition the LF band power increases and it's considered parasympathetic instead of sympathetic as RSA falls in this band. Moreover because of the maximum stimulation of the baroreflex this .1 Hz breathing is considered to be vagal modulated and results in a reduction of stress response.